1. Field of the Invention
The invention relates in general to a fabrication method of an electronic device, and more particularly to a fabrication method of an electronic device using an amorphous carbon (α-C) layer to adjust the pattern pitch of a hard mask.
2. Description of the Related Art
As integrated circuit devices become smaller and smaller, all the steps of a general semiconductor manufacturing process need to be adjusted to reach the required integration. For example, the thickness of the photoresist layer is reduced to increase the resolution of the pattern in the microlithography process. Or, a photolithographic machine with 193 um deep ultraviolet (DUV) is used to achieve the resolution of 50 nm above. However, the substrate can not be well shielded by the thinner photoresist layer when the etch selectivity is not increased relatively. Moreover, when a photolithographic machine with 248 um DUV is used to replace the photolithographic machine with 193 um DUV, the cost is increased and the reflectivity at the interfaces of films is increased. As a result, the transfer quality of the photoresist pattern is lowered.
Furthermore, a spacer and a hard mask (generally made of an oxide layer, such as silicon dioxide (SiO2) or silicon nitride (SiN)) formed between the photoresist layer and the substrate are used for improving the pattern transfer accuracy and the line-width. However, the conventional hard mask can not be used in some materials. In the process of removing the photoresist layer and the mask, several etching steps with different selectivity need to be performed. Therefore, the manufacturing time is increased, and the process becomes more complicated. Moreover, the hard mask may result in pollution in the following process after removed.